Ensure Renovate updates itself regularly (#6)

The `github-actions` manager should also work for Gitea Actions. It is
the same syntax.

As per Discord conversation, unpin the Docker digest for Renovate.

Signed-off-by: justusbunsi <sk.bunsenbrenner@gmail.com>

Reviewed-on: https://gitea.com/gitea/renovate-config/pulls/6
Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-committed-by: justusbunsi <sk.bunsenbrenner@gmail.com>

renovate.json

@@ -2,6 +2,14 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": ["gitea/renovate-config"],
   "dependencyDashboard": true,
+  "enabledManagers": [
+    "github-actions"
+  ],
+  "github-actions": {
+    "fileMatch": [
+      "^\\.gitea/workflows/renovate\\.yml$"
+    ]
+  },
   "packageRules": [
     {
       "description": "use fix scope for renovate updates",